In this case, the most valuable energy card ever is simply a reprint of the HeartGold & SoulSilver darkness energy, but critically, this version from Call of Legends is holofoil meaning its value ratchets up considerably
Dusk // Dawn : The Dawn side allows you to return all creature cards with power 2 or less from your graveyard to your hand
It is one of the best things you can pair with a Piledriver, you thought that card was scary before
Machina Fortress X EARTH Level 7 [ Machine / Effect ] ATK 2500 DEF 1600 You can discard Machine monster(s) whose total Levels equal 8 or more, then Special Summon this card (from your hand or GY)
Giving yourself hexproof can actually decide games against decks that must target you in order to win
We have lifelink, deathtouch, mass-pump for flying creatures (who arent easily blocked), and a way to create more flying creatures